Membrane fluid pump

ABSTRACT

A membrane fluid pump includes a rotatable drive shaft. The shaft is equipped with a number of eccentrics arranged axially along the shaft. The membrane fluid pump further comprises a set of connecting rods connected to each of the eccentrics. Each connecting rod is attached between one of the eccentrics on the shaft and a corresponding membrane so that each of the connecting rods is arranged to transfer a rotating movement of the shaft to a reciprocating movement pattern of the corresponding membrane. Each of the eccentrics and the connecting rods are arranged such that all of the membranes will reciprocate with a phase shift evenly distributed over a 360 degree rotation of the drive shaft, and wherein all of the eccentrics are rotationally offset to each other with an angle so that they are evenly distributed over a 360 degree rotation of the drive shaft.

TECHNICAL FIELD

The present invention relates generally to membrane fluid pump. Moreparticularly, the present invention relates to a membrane pump asdefined in the introductory parts of claims 1.

BACKGROUND ART

In air sampling scenarios for different pollutants and differentanalysis methods, the air flow rate through the samplers is importantfor the performance of a correct measurement with a sampler. To providea reliable air flow membrane pumps are often used. Different samplertypes, however, often require different flow rates. For the membranepump to function with different sampler types the pump will thus need tooperate with different speed.

A normal membrane pump has two membranes, each membrane being driven bya separate connecting rod. The connecting rods for the two membranes areoften driven by a common drive shaft with a cam arrangement so that themembranes will be driven with a phase shift of 180 degrees to each otherso that they will produce a fairly even flow rate. The two connectingrods are often connected to a single eccentric resulting in heavyvibrations in the pump.

The reciprocating nature of connecting rods in a membrane pump will leadto vibrations in the pump and an uneven torque for the motor driving theconnecting rods. Vibrations and an uneven load for driving the membranepump will wear the pump so that service will be required on a regularbasis. Vibrations will also affect the sampling negatively if thevibrations reach the sampler. The motor driving the pump will also beaffected by the vibrations and need service or replacement at a regularbasis. The motor will further be negatively influenced by the unevenload from the membrane pump leading to decreased lifetime of the motor.

A solution to solve the vibrational problems of traditional membranepumps is suggested in CN210326534Y, where a pump with eight membranesconfigures in two levels is presented. All membranes are driven bypistons connected to a common drive shaft with a cam profile controllingthe phase of the membranes. Each level with four membranes are driven bythe drive shaft to pump during with two membranes at a time 90 degreesphase shifted. The cam shape of the drive shaft is made so that eachopposing pistons will be in their outer and inner positions,respectively, at the same time, thereby balancing/neutralizing the massmovements of the pistons. The lower level is an exact copy of the upperlevel.

A drawback with the configuration of CN210326534Y is that only twopulses per revelation of the drive shaft is achieved by the eightmembranes and eight pump chambers. The two pulses are further producedduring the first 180 degrees of a piston revolution. A vibration freemovement is thus achieved on the expense of a very uneven flow. The camshape of the drive shaft and will also inflict a very uneven load forthe pump engine reducing energy efficiency of the pump. The pistons inCN210326534Y are further fastened in the drive shaft by rigid ringbearings, producing a movement where the piston angle is changedradically during each piston reciprocation.

There is thus a need for an improved membrane fluid pump that vibratesless during operation to avoid disturbing measurements and reducing theneed for service and that is easier to drive.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the current state ofthe art, to solve the above problems, and to provide an improvedmembrane fluid pump producing less vibrations and being easier to drive.These and other objects are achieved by a membrane fluid pump,comprising a drive shaft rotatable within said fluid pump. The shaft isequipped with a number of eccentrics distributed axially along theshaft. The membrane fluid pump further comprises a set of connectingrods being connected to each of the eccentrics, wherein each connectingrod is attached between one of the eccentrics on the shaft and amembrane, so that each of the connecting rods is arranged to transfer arotating movement of the shaft to a reciprocating movement pattern ofeach of the membranes. Each connecting rod and corresponding membraneoperates in an individual pump chamber. Each of the eccentrics and theconnecting rods are arranged in such a manner that all of the membraneswill reciprocate with a phase shift evenly distributed over a 360 degreerotation of the drive shaft, and all of the eccentrics are rotationallyoffset to each other with an angle so that they are evenly distributedover a 360 degree rotation of the drive shaft.

By driving different eccentrics with offset angle evenly distributedover 360 degrees (e.g. 0 and 180 degree for 2 eccentrics) the massmovement in the radial direct to the drive shaft of the first set ofconnecting rods is the opposite to the second set of connecting rods.The centre of mass in the radial direction to the crank shaft is thusconstant during the movement of the connecting rods and thereby themembranes. This leads to a vast reduction in vibrations compared tonormal membrane pumps with only one eccentric and one set of connectingrods. Since all membranes reciprocate in succession with a phase shiftthat is evenly distributed over 360 degrees, the heavy pulsationcharacteristic to membrane pumps is greatly reduced. Also the load forthe engine is evenly distributed, reducing the energy needed to drivethe pump.

The membrane fluid pump will due to the large number of membranes have aredundancy. If one membrane fails, others will still work as long as themembrane valve is closed.

The membrane pump according to the invention each eccentric may havethree connecting rods attached, each connected to one membrane. In thatway the membrane pump may be driven by a three phase electrical motorsimplifying acquisition of a motor for driving the pump. This motor maybe equipped with a rotary encoder, such as a set of Hall sensors inorder to measure and control motor speed. It is further an advantage toenable to use standardized electrical motors if the motor has to bereplaced, making it easier and cheaper to find a new motor.

The shaft of the membrane fluid pump may be equipped with twoeccentrics, wherein each of the two eccentrics is connected to a set ofthree connecting rods. By offsetting the two eccentrics by 180 degreesthe membranes will reciprocate with a successive phase shift of 60degrees while at the same time constantly keeping an unchanged massbalance in the radial direction of the drive shaft reducing vibrationsand keeping a constant load for driving the pump.

According to other embodiments of the invention the shaft may beequipped with more than two eccentrics, and the number of connectingrods connected to each eccentric is one more than the number ofeccentrics. The shaft may be equipped with more than two eccentrics, andthe number of connecting rods connected to each eccentric is one lessthan the number of the eccentrics. The same advantages are achieved withsuccessive membrane movements evenly distributed over 360 degrees whilekeeping mass balance during operation.

The membrane fluid pump according to the present invention may howeverin other embodiments comprise each eccentric to have more than threeconnecting rods attached. The same advantages as for the embodimentsalready discussed are achieved also with sets of connecting rods havinge.g. five connecting rods and five 5 membranes. The advantage withhaving a greater number of connecting rods and membranes is further thatthe flow rate will be smoother as the cycles of each connecting rod andmembrane will have a smaller phase shift to the next connecting rod andmembrane. With five connecting rods connected to an eccentric, theconnecting rods will have a phase shift of only 72 degrees compared to120 degrees when having three connecting rods connected to an eccentric.

It is further preferred that the sets of connecting rods connected toeach eccentric are arranged to reciprocate from the same axial positionalong the drive shaft. Each of the sets of connecting rods may e.g. befastened to a ball bearing enveloping the eccentric of the drive shaftso as to create a crank effect. If the connecting rods are evenlydistributed around the circular ball bearing, the phase shift betweenneighbouring connecting rods will be 360 degrees divided by the numberof connecting rods.

According to a still further embodiment of the present invention themembrane fluid pump comprises a drive shaft rotatable within the fluidpump, a number of sets of connecting rods attached to the drive shaft soas to reciprocate with a phase shift evenly distributed over a 360degree rotation of the drive shaft, wherein each connecting rod isarranged to drive a separate membrane. The number of sets of connectingrods is equal to the number of connecting rods in each set, and each setof connecting rods are driven out of phase in relation to each otherwith 360 degrees divided by the number of sets of connecting rods. Thenumber is greater than two. In this embodiment each connecting rods willoperate in phase with one connecting rod in each connecting rod set,where the connecting rods that operate in phase will have a phase shiftevenly distributed over 360 degrees. In that way the centre of mass inthe radial direct will stay unaffected by the crank movements leading toa vibration free operation of the membrane fluid pump.

The membrane fluid pump of the invention may further comprise an inletvalve and an outlet valve for each membrane. The inlet valve and outletvalve are opening and closing by the difference in fluid pressure thesaid membrane exerts when moving in a reciprocating pattern. If severalmembrane inlets and outlets are connected in a manner so that the fluidpressure change from each of said reciprocating membrane contributes tothe opening and closing mechanism of said inlet and outlet valves. Priorart membrane pumps may have pressure difference driven inlet and outletvalves which are in an undefined state when no pressure difference ispresent. A certain pressure difference threshold is required to putthose valves in either open or closed state, therefore a certainmembrane reciprocating speed is required before such a pump will operateproperly. A pump with normally closed valves will be able to operate atmuch lower membrane reciprocating speed enabling lower flow rates.

According to a further embodiment of the present invention the shaft ofseveral pump modules are connected in series, increasing the number oftotal membranes, thereby either further increasing total flow andreducing the pulsation if the membranes are evenly phase shifted amongthe modules or connecting several membranes in series, achieving aseveral stage vacuum pump or compressor. The shaft may further beequipped with a gearbox to control the speed of the shaft and to reducethe rotational speed range of the motor driving the shaft.

The flow rate of the membrane fluid pump may further be controlled byenabling and disabling the opening and the closing of valves of separatemembranes. A control unit connected to the pump controlling the valveswill thereby be able to effectively control the flow of the membranefluid pump. The flow rate of the membrane fluid pump may further becontrolled by changing the offset of the eccentrics thereby changing thedisplacement volume of each membrane stroke. If a membrane is broken,the phase shift between the remaining membranes may be controlled sothat the strokes of the remaining membranes are evenly distributed overa rotation and thereby produces a pulse-free flow. The change may eitherbe semi-permanently made when assembling the pump at the manufacturingstage or the eccentrics may be arranged to be controlled so as to changethe displacement volume by e.g. changing the angle that the connectingrod is attached to the eccentric. The flow rate of the membrane fluidpump may further be controlled by changing the dead volume of themembrane cavity.

According to a further embodiment of the invention the inlets and/oroutlets from all membranes of the membrane fluid pump are interconnectedvia a cavity, so as to reduce interference between pump heads. A pumphead comprises a reciprocating membrane connected to a cavity furtherconnected to an inlet valve and an outlet valve, where said membraneinflates said cavity while said inlet valve is open and deflates saidcavity while said outlet valve is open.

As presented above, the problems of the prior art are thus addressed bythe fluid membrane pump of the present invention. A vibration freeoperation of the membrane fluid pump is facilitated due to a centre ofmass in the radial direction of the drive shaft that does not changeduring operation. This also leads to a membrane fluid pump that iseasier and smoother to drive for a drive motor. A pulse free flow isalso achieved since the reciprocating movements of the membranes arephase shifted evenly distributed over a rotation.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the [element, device,component, means, step, etc.]” are to be interpreted openly as referringto at least one instance of said element, device, component, means,step, etc., unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, as well as additional objects, features andadvantages of the present invention, will be more fully appreciated byreference to the following illustrative and non-limiting detaileddescription of preferred embodiments of the present invention, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is schematic view of the cross section of one of the sets ofconnecting rods of a membrane fluid pump according to the presentinvention.

FIG. 2 is schematic view of a cross section along the drive shaft of themembrane fluid pump of the present invention showing the principle ofthe invention.

FIG. 3 is perspective view showing two neighbouring connecting rods inthe direction of the drive shaft. The two visible connecting rods belongto two different connecting rod sets.

FIG. 4a is a representation of the pulsation of the output flow from apump according to the prior art.

FIG. 4b is a representation of the pulsation of the output flow from thepump according to FIG. 2 and FIG. 3.

FIG. 5 is table showing different possible configurations for anoptimized multi membrane pump according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is schematic view of the cross section of one of the sets ofconnecting rods 3, 4 of a membrane fluid pump 1 according to theinvention. The connecting rods 3, 4 reciprocate with a phase shiftevenly distributed over a 360 degree rotation of the drive shaft 2. Asthere are three connecting rods 3, 4 in the embodiment of FIG. 1, theindividual connecting rods 3, 4 with their respective membranes 3″, 4″will be phase shifted 120 degrees apart from each other. Each connectingrod 3, 4, of the set of connecting rods 3, 4 is arranged to drive aseparate membrane 3″, 4″. The connecting rods 3, 4 of the set ofconnecting rods 3, 4 are fastened to an eccentric 7 offset to driveshaft 2. The connecting rods 3, 4 are evenly distributed around thecircumference of the eccentric to accomplish a reciprocating movementfor each connecting rod 3, 4 phase shifted 120 degrees to the next.

FIG. 2 shows the membrane pump 1 of the present invention in a crosssection along the drive shaft 2 showing the principle of the inventionwith having two connecting rod sets 3, 4 arranged to actuate theirrespective membranes 3″, 4″ in counter phase to each other, i.e. with aphase shift of 180 degrees. The drive shaft is connected to a motor 8for driving the pump. As can be seen in FIG. 2 when one connecting rod 3of one connecting rod set is in its upper end position upwards, theneighbouring connecting rod 4 in the direction of the drive shaft 2 isin its lower end position thereby eliminating any the combined massmovement in the radial direction to the drive shaft 2.

The connecting rods 3, 4 of each of the first set of connecting rods 3and the second set of connecting rods 4 are arranged to reciprocate fromthe same position along the length of said drive shaft but phase shifted180 degrees to eliminate any average mass movement in the radialdirection of the drive shaft. FIG. 2 further shows the motor 2 drivingthe membrane fluid pump.

The skilled person realizes from the claims and the summary of theinvention that the embodiment of FIG. 2 could be extended with furthersets of connecting rods. Any number of sets of connecting rods attachedto the drive shaft may be arranged to reciprocate with a phase shiftevenly distributed over a 360 degree rotation of the drive shaft. Eachconnecting rod is arranged to drive a separate membrane, and the numberof sets of connecting rods is then chosen to be equal to the number ofconnecting rods in each set of connecting rods. If the different sets ofconnecting rods are driven out of phase in relation to each other with360 degrees divided by said number of sets of connecting rods theaverage mass movement in the direction of the drive shaft will beeliminated.

FIG. 3 is perspective view showing two neighbouring connecting rods 3, 4in the direction of the drive shaft 2 of the fluid membrane pump 1. Thetwo visible connecting rods belong to two different connecting rod setsattached to two different eccentrics 7. The membranes (not shown) areplaced over the holes 5, 6 and are driven by the connecting rods 3, 4 incounter phase to each other to eliminate any average mass movement inthe radial direction to the drive shaft. FIG. 3 reveals a furtheradvantage of the present invention. All chambers angled in the samedirection, in the configuration of FIG. 2 and FIG. 3 two of the sixchambers, may be serviced by removing one single “cylinder head” or lid.

FIG. 4a shows a representation of the pulsation of the output flow froma pump according to the prior art. The solid lines show the pulsesinduced by the eight membranes of CN210326534Y, while the dashed linerepresent the combined average flow. FIG. 4b shows the pulsation of theoutput flow from the pump according to FIG. 2 and FIG. 3. As can be seenthe pulsation is much smother from the pump according to the presentapplication than from the prior art pump. The reason for this is thatthe membranes of CN210326534Y only pump at 90 and 180 degrees, leavinghalf a revolution of the crank shaft without any induction of pulses bythe membranes.

FIG. 5 shows different possible embodiments of the pump according to thepresent invention. The possible embodiments are marked in the table witha box and grey background. All the combinations of the table wouldproduce a functioning pump, but only the combinations marked with a boxand grey background achieve all advantages of the invention, i.e. apulsation free pump where the reciprocation of the pistons and membranesare neutralized so that no net mass movement is present during rotation.In other words, the centre of mass is always kept along the centre axisof the drive shaft 2 during operation of the pump. FIG. 5 shows thatthis configuration is possible with

-   -   three rods per eccentric and two eccentrics,    -   four rods per eccentric and three eccentrics, and    -   five rods per eccentric and four eccentrics.        The advantages shown above in accordance with the invention is        thus achieved by a pump according to what is described above        having N rods and N−1 eccentrics, when N>3.

It is understood that other variations in the present invention arecontemplated and in some instances, some features of the invention canbe employed without a corresponding use of other features. Accordingly,it is appropriate that the appended claims be construed broadly in amanner consistent with the scope of the invention.

1. A membrane fluid pump comprising: a drive shaft rotatable within saidmembrane fluid pump, a plurality of eccentrics arranged axially alongthe drive shaft, a set of connecting rods being connected to eacheccentric, wherein each connecting rod of said set of connecting rods isattached between one of said plurality of eccentrics on said drive shaftand a corresponding membrane, so that each of said connecting rods isarranged to transfer a rotating movement of said drive shaft to areciprocating movement pattern of the corresponding membrane, whereineach eccentric and said connecting rods are arranged such that all ofsaid membranes will reciprocate with a phase shift evenly distributedover a 360 degree rotation of said drive shaft, and wherein all of saideccentrics are rotationally offset to each other with an angle so thatthey are evenly distributed over a 360 degree rotation of said driveshaft.
 2. (canceled)
 3. The membrane fluid pump according to claim 1,wherein the connecting rods of each set of connecting rods are arrangedto reciprocate from a same axial position along said drive shaft.
 4. Themembrane fluid pump according to claim 1, wherein each of saideccentrics has a ball or a sleeve bearing between said drive shaft andsaid set of connecting rods attached to that eccentric.
 5. The membranefluid pump according to claim 1, further comprising a pump headincluding an inlet valve and an outlet valve or a valve combining inletand outlet valve functionality for each membrane fluid pump.
 6. Themembrane fluid pump according to claim 5, where said each inlet valveand outlet valve are opening and closing by the fluid flow that the saidmembrane induces when moving in the reciprocating movement pattern. 7.The membrane fluid pump according to claim 5, where said each inletvalve and outlet valve are opening and closing as an active mechanism.8. The membrane fluid pump according to claim 5, wherein opening andclosing of each inlet valve and outlet valve is in response to apredetermined pressure difference threshold.
 9. The membrane fluid pumpaccording to claim 8, including membrane inlets and outlets incommunication with corresponding inlet and outlet valves, wherein theplurality of membrane inlets and outlets are connected such that thefluid pressure change produced by each of said reciprocating membranescontributes to the opening and closing of said inlet and outlet valves.10. A plurality of membrane fluid pumps according to claim l, whereinthe drive shafts of at least two of the plurality of membrane fluidpumps are connected in series so as to increase the total number ofmembranes.
 11. The plurality of membrane fluid pumps according to claim10, wherein the drive shafts of at least two of the plurality ofmembrane fluid pumps are connected in series by a gearbox to permit thedrive shafts of the at least two of the plurality of membrane fluidpumps connected in series to have different rotational speeds.
 12. Themembrane fluid pump according claim 8, wherein the flow rate of themembrane fluid pump is controlled by enabling and disabling opening andclosing inlet and outlet valves of different membranes.
 13. The membranefluid pump according to claim 1, wherein rotation of the drive shaft andthe eccentrics arranged axially along the drive shaft produce a membranestroke for respective membranes, and a flow rate of the membrane fluidpump is controlled by changing an offset of at least some eccentricsthereby changing a displacement volume for respective membrane strokes.14. The membrane fluid pump according to claim 5, wherein the pump headincludes a pump head cavity and a flow rate of the membrane fluid pumpis controlled by changing a dead volume of the pump head cavity.
 15. Themembrane fluid pump according to claim 9, wherein at least one of themembrane inlets and outlets from all membranes are interconnected via acavity so as to reduce interference between opening and closing of inletvalves and outlet valves in said pump heads.